An apparatus for reducing the extent of displacement between adjacent vertebrae is shown in U.S. Pat. No. 4,611,581 to Steffee. That apparatus includes a pair of rigid plates, which are attached to opposite sides of the spinous process of the human spine. The plates are attached to the spine by bolts with coarse threads on one end and machine threads on the other. The coarse threads of the bolts are first screwed into the spine. The plates are then placed over the machine-threaded portion of the bolts, which are then held in place by nuts, threaded over the top of the plates. A displaced vertebra is relocated by pulling the vertebra toward the plate by tightening the nut on the bolt that holds the displaced vertebra.
A problem with this design is that it leaves a rather high profile of metal extending above the spine. The following invention is one solution to this problem.